Add mus::mojom::ChannelHandle for passing IPC::ChannelHandle via mojo IPC.

components/mus/public/interfaces/channel_handle.mojom

Index: components/mus/public/interfaces/channel_handle.mojom
diff --git a/components/mus/public/interfaces/channel_handle.mojom b/components/mus/public/interfaces/channel_handle.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..d78a53f597743a55eb609456a35cafc84e097a68
--- /dev/null
+++ b/components/mus/public/interfaces/channel_handle.mojom
@@ -0,0 +1,13 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module mus.mojom;
+
+// See IPC::ChannelHandle in src/ipc/ipc_channel_handle.h
+struct ChannelHandle {
+  string name;
+
+  // On POSIX, it is one endpoint of a socket pair. On Windows, it is not used.
+  handle socket;
+};